Thanks, Jim, that's one reason! But while you have the view focused without wearing your glasses, why isn't that setting good enough for everything in the heavens above? Why do you have to refocus when you look at something else, or when you take a look another day? The only reason I can come up with, and it doesn't seem like a complete answer, is that the atmosphere might act like a lens and distort the view depending on the angle of the telescope to the curvature of the atmosphere. Is that the reason? Does Hubble need to focus when it points to a different target? -- Joe
This question I can at least partially answer. I wear some pretty strong glasses (4.5 diopters). Sometimes I view through the telescope with glasses removed. The focus adjustment allows me to make this work (well, the astigmatism is still frustrating...).
Jim
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